The present invention relates to a link belt for the power transmission for a continuously variable automatic transmission (CVT).
A continuously variable transmission consists generally of e.g., a starting unit, a forward/reverse driving unit, an intermediate shaft, a differential, hydraulic and electronic control devices as well as a variator.
According to the state of the art, the variator comprises a primary and a secondary pulley, also called primary and secondary sides, wherein these pulleys are formed by cone pulleys that are arranged in pairs. Furthermore a variator is equipped with a torque-transmitting continuously variable element, which runs between the two cone pulley sets.
In such a transmission, the current gear ratio is defined by the running radius of the continuously variable element, which in turn is a function of the axial position of the cone pulleys.
A continuously variable element, in particular for higher power engines, consists according to the state of the art of individual links, which serve the actual power transmission, and of so-called ring packages. Such link belts consist of a plurality of individual metal elements, which are mated and which are held on both sides of the radial plane of the finished link belt by one flexible ring package each.
These ring packages can consist of high-strength stainless steel and advantageously contain nine to twelve rings that are arranged concentrically to each other.
The ring packages hold the individual links together and therefore must absorb considerable forces, in particular with small radii, which the strip must handle at certain gear ratios.
The forces increase with the torque that is to be transmitted. The transmission capacity of a link belt currently lies around 300 Nm.
During operation, the ring packages are exposed to constant bending stress: With one revolution of the link belt around the variator the strip, transitions from a straight movement into a radius movement around the primary pulley, subsequently again into a straight movement and then into a radius movement around the secondary pulley. This constant variation of the bending radius sets a limit on the reinforcement of the ring packages, which therefore cannot be reinforced indefinitely.
For this reason it is not possible to reinforce the ring packages without simultaneously increasing the rigidity of the entire link belt, which in turn during operation increases the smallest possible running radii and the friction losses unfavorably.
The present invention is based on the task of presenting a link belt, which can transmit more torque without impairment of its flexibility.
Furthermore, power loss is to be reduced.
Accordingly, separating absorption of the radial forces generated on the links from the actual xe2x80x9cguidancexe2x80x9d of the links is proposed.
Similar to the link belt known from the state of the art, the link belt of the invention comprises a plurality of individual links and two ring packages. The first ring package serves to guide of the links. The individual links are therefore equipped with appropriately designed guidance brackets and are arranged behind the other on the first ring package. Pursuant to the invention, an additional ring package is provided, which is arranged on the outside around the link belt and is mounted on one side for example in a fixed pivot of the strip in such a way that it can no longer rotate together with the strip. Nonetheless, it can follow the strip""s adjusting movement.
Since this second ring package runs no longer constantly around the variator, but only follows the motion due to changes in the gear ratio, it can be considerably more strongly designed than has been possible in the past. By contrast, the first ring package, which holds the links, can be designed accordingly weaker since the outer, standing ring package absorbs the main forces.
In order to guarantee this functionality, a bearing, via which the radial forces are transmitted from the actual link belt to the outer ring package, is provided between the actual link belt and the outer ring package.
Pursuant to the invention, the first ring package to guide the links is arranged in the center of the links, so that rollers can be accommodated between the second outer ring package and the first ring package for guiding the links. A xe2x80x9ccorrugated spring bandxe2x80x9d or a movable plastic cage can be used for example as cages for these rollers.
Pursuant to a variation of the invention, instead of the rollers a flexible xe2x80x9cslide railxe2x80x9d is employed. It can consist of bearing material, preferably plastic, and covers the entire circumference.
The slide rail can be supplied with oil under pressure via the outer ring package, which is fastened in the housing, in order to ensure lubrication.
Alternatively, instead of the slide rail, a lubricating film with oil under pressure can be set up between the outer and inner ring packages.
Since the strip does not follow the ideal path, but rather deviates from it, according to the invention, a guiding sleeve is provided in the area of the actual straight stretch between the primary and secondary side as a guide. This guiding sleeve can be employed at the same time as an attachment for the fixed outer ring package in order to prevent the inner ring package from lifting off the outer ring package.